But at just three years old, it would be more than understandable if Kate Middleton and Prince William's daughter had some LOL-worthy moments at some point in the day.

Look no further than when Princess Charlotte arrived at St. George's Chapel to perform her duties as a bridesmaid.

In a photo going viral, Prince George and Prince Louis' sister stuck out her tongue long enough for photographers to snap a photo. But as it turns out, Prince Harry totally did the same thing years ago.

Photos

The newlywed was captured doing something very similar to photographers in 1988. While it wasn't for a wedding ceremony, the occasion was still a big one as his cousin Princess Beatrice of York was born.

Ultimately, Princess Charlotte was quite the hit at St. George's Chapel as she walked in wearing a white dress from Givenchy Haute Couture Atelier, made with Ivory silk Radzimir. The dress featured short puff sleeves and a double silk ribbon in the back.

To finish the look, Kate's only daughter wore Aquazurra shoes, which were monogrammed and dated—a gift from Meghan—and a flower crown.

As for that wave on the steps of St. George's Chapel? Yes, we're still smiling too.

Watch E!'s five-hour Live From the Royal Wedding coverage Saturday, 19 May starting at 10 a.m. and again later that day.

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